Air breathing turbine engines typically include, as major components, a turbine wheel coupled to a rotary compressor. A combustor receives compressed air from the compressor as well as fuel from a fuel source and burns the same to provide hot gases of combustion to drive the turbine wheel.
Many such systems employ so-called "annular" combustors which typically include a somewhat toroidal-shaped combustion chamber centered about the rotational axis of the turbine wheel and there are provided a plurality of circumferentially or angularly spaced fuel injectors which inject fuel into the annular combustion space. In the usual case, the injectors are of two different types. One type is a so-called "main" injector which is utilized during normal operation. The other type is a so-called "start" injector which is utilized only during the starting sequence for the turbine.
Generally speaking, the start injectors are configured to provide for good atomization of the fuel by means of pressure atomization because at start up, the velocity of compressed air received from the compressor is relatively low and cannot be relied upon to enhance atomization.
Frequently, to achieve the enhanced atomization of fuel that is required at low engine rotational speeds, relatively high volumes of fuel are pumped through the start injectors. However, this may result in local overfueling which in turn causes combustion inefficiencies and hot streaks or hot spots which can damage the combustor.
This difficulty may be exacerbated when it is necessary to start the turbine at high altitude. In such a case, the effect of so-called "altitude head" causes fuel flow at the bottom of a manifold feeding the injectors to be significantly greater than fuel flow at the top of the manifold. This results in hot spot generation near the bottom of the annular combustor where start injectors are frequently located as well as poor flame propagation around the annular combustor to the top thereof. Consequently, not only must one face the difficulty of hot spots, starting is not as reliable as may be desired because of poor flame propagation.
The present invention is directed to overcoming one or more of the above problems.